This is a multicenter chemoprevention seven year clinical trial using Finasteride to reduce the incidence of prostate cancer in healthy men. Finasteride is a 5-alpha reductase inhibitor which may play a pivotal role in the initialization and progression of prostate cancer. After an initial run-in period, volunteers without evidence of prostate enlargement and with a normal PSA will be randomized to receive either daily Finasteride or matched placebo for 7 years or until the development of prostate-related symptoms